1. Field of the Invention
The invention relates to a method of forming a polymer with a functional group. In particular, it relates to a nitroxy functional polymer containing a low molecular weight polydiene block which is easy to handle at ambient temperatures, and will be described with particular reference thereto.
2. Discussion of the Art
Rubber modified polymers have been produced from vinyl aromatic monomers by a number of processes for the purpose of improving impact resistance. Typically, a rubber is blended with a polymerized vinyl aromatic monomer, or alternatively, the vinyl aromatic monomer is polymerized in the presence of a rubber. In the latter method, the vinyl aromatic monomer is partially graft polymerized onto the rubber. Rubber modified copolymers of vinyl aromatic monomers have also been produced, such as acrylonitrile-butadiene-styrene (ABS). ABS copolymers have been produced using polymerization processes such as bulk-suspension, continuous bulk, and emulsion.
U.S. Pat. No. 5,721,320 discloses a free radical bulk polymerization process for producing a rubber modified polymer from a vinyl aromatic monomer. A conjugated diene rubber, such as polybutadiene, having at least one stable free radical group, such as a nitroxy group, is combined with a vinyl aromatic monomer and optionally a copolymerizable monomer, such as acrylonitrile, under free radical bulk polymerization conditions. The vinyl aromatic monomer polymerizes to form a matrix phase and copolymerizes with the conjugated diene rubber such that a grafted vinyl aromatic-diene block copolymer rubber is formed in situ. It is known to use epoxy-functionalized nitroxyl compounds, as disclosed in U.S. Pat. No. 6,444,754.
However, for some applications, the desired molecular weight of the functionalized polybutadiene is so low that it is impractical to handle at ambient temperatures, due to its viscous state.
The present invention provides a new and improved nitroxy-functional polymer and method of forming, which overcome the above-referenced problems and others.